Fukushima reactor core battle continues

Tokyo Electric Power Co (TEPCO) has battled furiously today to prevent critical overheating of the core of the Fukushima nuclear plant's No 2 reactor.

Following the failure of back-up diesel generators designed to maintain coolant flow, it fell to an emergency "fire pump", to keep the situation under control. This unorthodox method, a TEPCO official explained to the BBC, "had been invented by the team on the ground at Fukushima".

The fire pump itself then ran out of fuel, at which point the fuel rods spent 140 minutes fully exposed.

All the plant's reactors were shut down following Friday's 9.0-magnitude earthquake, but still require a period of cooling to deal with any residual heat.

Reactors No 1 and 3 lost their external roofs on Saturday and Monday, respectively, as superheated steam vented from their overheating reactor cores broke down into an explosive mix of hydrogen and oxygen.

This structural damage is purely cosmetic, and the radioactive material released into the atmosphere poses a negligable threat to the population. However, it's suspected that Monday's blast in the No 3 reactor may have knocked out four other emergency fire pumps whose services TEPCO would doubtless have welcomed.

Workers managed to raise the water level inside the No 2 reactor this afternoon, but it later dropped, re-exposing the rods.

The Japanese government later "confirmed that Japan has asked the International Atomic Energy Agency (IAEA) to provide expert help at its damaged nuclear plant", Reuters reports.

If the No 2 reactor's core does melt down, its steel containment vessel is designed to safely trap radioactive material. ®